From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4DFEEC04AB4 for ; Fri, 17 May 2019 12:59:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 147AA2087B for ; Fri, 17 May 2019 12:59:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558097961; bh=kaZeVHl/xgSjpNltSXEH4wuOiYmO0vWqioPlSOG8/eg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=HIzPY4doFOPnOUCVV3ywsvxjTYKdv724ho9/6ADYj0d/gqEv3Ngh6liVUPohkmCf1 YxV0Xm4oVj4u/Z13/SHsNEo6AqnDlxHpXqUzHQTJdS3CGWRMhx5qG3oYW11gcbKWz8 ILYf8tLSVaD/Wnzt8wFbDeyqsSyAQ2Rk9E+36OTk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728389AbfEQM7U (ORCPT ); Fri, 17 May 2019 08:59:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:36736 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728374AbfEQM7U (ORCPT ); Fri, 17 May 2019 08:59:20 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5168EAB92; Fri, 17 May 2019 12:59:18 +0000 (UTC) Date: Fri, 17 May 2019 14:59:16 +0200 From: Michal Hocko To: Alexander Potapenko Cc: akpm@linux-foundation.org, cl@linux.com, keescook@chromium.org, kernel-hardening@lists.openwall.com, Masahiro Yamada , James Morris , "Serge E. Hallyn" , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Jann Horn , Mark Rutland , Souptick Joarder , Matthew Wilcox , linux-mm@kvack.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH v2 3/4] gfp: mm: introduce __GFP_NO_AUTOINIT Message-ID: <20190517125916.GF1825@dhcp22.suse.cz> References: <20190514143537.10435-1-glider@google.com> <20190514143537.10435-4-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190514143537.10435-4-glider@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: [It would be great to keep people involved in the previous version in the CC list] On Tue 14-05-19 16:35:36, Alexander Potapenko wrote: > When passed to an allocator (either pagealloc or SL[AOU]B), > __GFP_NO_AUTOINIT tells it to not initialize the requested memory if the > init_on_alloc boot option is enabled. This can be useful in the cases > newly allocated memory is going to be initialized by the caller right > away. > > __GFP_NO_AUTOINIT doesn't affect init_on_free behavior, except for SLOB, > where init_on_free implies init_on_alloc. > > __GFP_NO_AUTOINIT basically defeats the hardening against information > leaks provided by init_on_alloc, so one should use it with caution. > > This patch also adds __GFP_NO_AUTOINIT to alloc_pages() calls in SL[AOU]B. > Doing so is safe, because the heap allocators initialize the pages they > receive before passing memory to the callers. I still do not like the idea of a new gfp flag as explained in the previous email. People will simply use it incorectly or arbitrarily. We have that juicy experience from the past. Freeing a memory is an opt-in feature and the slab allocator can already tell many (with constructor or GFP_ZERO) do not need it. So can we go without this gfp thing and see whether somebody actually finds a performance problem with the feature enabled and think about what can we do about it rather than add this maint. nightmare from the very beginning? -- Michal Hocko SUSE Labs